The invention relates to cooling and heating. More particularly, the invention relates to economized air conditioning, heat pump, or refrigeration systems.
U.S. Pat. No. 6,955,059 discloses an economized vapor compression system with different modes of unloading. Additionally, commonly assigned U.S. Pat. No. 4,938,666 discloses unloading one cylinder of a bank by gas bypass and unloading an entire bank by suction cutoff. Commonly assigned U.S. Pat. No. 4,938,029 discloses the unloading of an entire stage of a compressor and the use of an economizer. Commonly assigned U.S. Pat. No. 4,878,818 discloses the use of a valved common port to provide communication with suction for unloading or with discharge for volume index (Vi) control, where Vi is equal to the ratio of the volume trapped gas at suction (VS) to the volume of trapped gas remaining in the compression pocket prior to release to discharge. In employing these various methods, the valve structure is normally fully open, fully closed, or the degree of valve opening is modulated so as to remain at a certain fixed position. Commonly assigned U.S. Pat. No. 6,047,556 (the '556 patent, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length) discloses the use of solenoid valve(s) rapidly cycling between fully open and fully closed positions to provide capacity control. The cycling solenoid valve(s) can be located in the compressor suction line, the compressor economizer line and/or the compressor bypass line which connects the economizer line to the suction line. The percentage of time that a valve is open determines the degree of modulation being achieved. U.S. Pat. No. 6,619,062 discloses control of scroll compressor unloading mechanisms based solely upon scroll compressor pressure ratio operation.
Nevertheless there remains room for further improvement in the art.